Electronic Structure of Titania Nanosheets with Vacancies Based on First-Principles Calculations

Abstract

Titania nanosheets (TNSs) are expected to lead to higher photocatalytic performance than bulk TiO2 because its high reactivity arises from the two-dimensional structure. While their electronic properties are considered to be easily affected by structural vacancies, the effects of vacancies in TNSs on the photocatalytic performance are not clear. In order to study them, we have performed first-principles molecular dynamics simulations for structure models of TNSs with several vacancies. First, we have calculated the electronic density of states and bandgap energies Eg. It has been found that Eg of our structure modes of TNSs with vacancies are larger than bulk anatase. This tendency is consistent with the experimentally observed relationship of Eg between TNSs and anatase. It has been clarified from non-adiabatic calculations that the existence of vacancies in TNSs causes spatial charge separation and leads to longer recombination time.

An Unusually Acidic and Thermally Stable Cesium Titanate CsxTi2–yMyO4 (x = 0.67 or 0.70; M = vacancy or Zn)

“…This result suggests that Ti atoms at the proximity of the vacancy sites could be specifically responsible for NH 3 LT desorption. (The formation of hydroxylated groups due to water adsorption around the □ sites is energetically favorable; 52,53 however, the adsorption of NH 3 has not been reported to the best of our knowledge.) Importantly, the observed increase in acidity upon HT desorption in Cs 0.7 ZnTO indicates the presence of other types of acid sites, which are not associated with the □ sites (also see the XPS results below).…”

Effects of defects on the electronic and optical properties of TiO 2 nanosheet

“…Early theoretical work proposes that the stablest polymorph is the L-TiO 2 one [29]. Researchers have carried out a series of studies on the L-TiO 2 nanosheet [30][31][32][33][34][35][36][37][38][39]. Wang et al find that strains could result in a significant change in the band gap and optical absorption of the L-TiO 2 nanosheet, improving its photocatalytic performance [34].…”

“…There have been several first-principles calculations on the electronic structures of TiO 2 nanosheets containing Ti and O vacancies. However, these calculations are based on the density functional theory (DFT) [35,36,38,48]. In this work, we systematically investigate vacancy defects in the L-TiO 2 nanosheet, including O vacancies (O v ), Ti vacancies (Ti v ) and Ti-O vacancies ((Ti-O) v ), by more advanced first-principles approaches, including the GW method and the Bethe-Salpeter equation (BSE) within the many-body perturbation theory, aiming to explore their effects on the quasiparticle band structures and optical properties of the L-TiO 2 nanosheet.…”